This invention relates to a method of inhibiting the growth of barium sulfate scaling by using a blend of (a) a polyphosphate with degree of polymerization between 6 and 21, and (b) a polyphosphate with degree of polymerization of 2-3.
Barium sulfate scaling is a problem encountered in several industrial processes, in particular papermaking, mining, and oil production. Barium and/or sulfate is found in wood, alum, and/or water (fresh, well, and seawater) that may be used in one or more of these manufacturing processes. A variety of scale inhibitors is used to reduce the incidence of barium sulfate scaling. The most effective among them are polyepoxysuccinic acid (see U.S. Pat. Nos. 5,062,962 and 5,368,740), polyvinylsulfonate (see U.S. Pat. No. 4,710,303) or other sulfonate containing polymers, and polyphosphates such as those shown in U.S. Pat. No. 5,468,393, which is hereby incorporated by reference.
These chemicals are more or less effective, depending on the severity of scaling conditions and presence of interfering ions such as H+ at low pH or polyvalent metals. In some cases the available chemicals are of only marginal efficacy and thus new inhibitor formulations with improved performance are desirable.
This invention relates to scale inhibiting compositions comprising:
(a) a polyphosphate with degree of polymerization between 6 and 21, and
(b) a polyphosphate with degree of polymerization 2-3.
Preferably a phosphino-polyacrylate is added to the composition.
The blends are particularly effective at inhibiting barium sulfate scale and provide economic advantages. Although (a) alone is an effective barium sulfate scale inhibitor, it is more expensive than (b), which is not effective alone as a barium sulfate scale inhibitor. It was unexpected that the blend, containing significant amounts of (b), would work as effectively as (a) alone. The 50/50 blend is particularly advantageous and exhibits synergism. The blends are more cost effective than using (a) alone. The invention also relates to a process for inhibiting barium sulfate scale in an open system subject to evaporation.
One of the polyphosphates, component (a), used in the scale inhibiting compositions, is a polyphosphate having a degree of polymerization between 6 and 21. Examples of such polyphosphates are sodium and potassium salts of hexamethaphosphate, preferably the sodium salts. The other polyphosphate, component (b), has a degree of polymerization of 2-3. Examples of such polyphosphates are sodium or potassium salts of tripolyphosphate or pyrophosphate. The polyphosphates are commercially available from FMC as Sodaphos, Hexaphos, and Glass H.
Barium sulfate scale inhibition is further improved by the addition of a polyacrylate scale inhibitor to the blend. Suitable polyacrylate scale inhibitors have an average molecular weight ranging from to 500 to 10,000. Suitable polyacrylate inhibitors include homopolymers and copolymers containing derived from monomers having alpha, beta-ethylenically unsaturated linkages such as acrylic acid, methacrylic acid, diacids such as maleic acid, and the like. When the inhibitor is a copolymer, the other component monomers can be any alpha, beta-ethylenically unsaturated monomer with either a non-polar group such as styrene or olefinic monomers, or a polar vinyl functional group such as acrylamide or acrylamide derivatives, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
Preferably, the polyacrylate inhibitor is a phosphino-polyacrylic acid, a modified polyacrylate. These products are sold under the tradename xe2x80x9cBelsperse 161xe2x80x9d or xe2x80x9cBelasol S-29xe2x80x9d by Ciba Geigy. Particularly preferred are phosphino-polyacrylic acid having an average molecular weight of 3000 to 4000.
Typically, the effective concentration of the polyacrylate inhibitor ranges from 0.05 to 50 ppm, preferably 0.5 to 10 ppm in treated water.
Preferably, a polyacrylate, containing phosphino linkages in its backbone, is added to the composition to further inhibit barium sulfate scaling. An example of such polyacrylates is Belsperse 161, having an average molecular weight of 2,800 to 3,800, sold by FMC.
Optional components, e.g. azoles, surfactants, dispersants, etc. may provide additional benefits in a finished product, but do not affect barium sulfate growth.
The optimum ratio of (a) and (b) depends on the composition of the liquid stream, in particular the concentration of Al+3 and other polyphosphate binding metal ions. The weight ratio of actives in (a) to (b) is typically from 1:9 to 9:1, preferably from 1:9 to 3:1, more preferably from 1:2 to 2:1, and most preferably about 1:1, based upon the total weight of (a) and (b). The solids content of (a) plus (b) is typically from 1 to 25 weight percent based upon the total weight of (a) and (b). These formulations are used in amounts of 1 to 50 ppm in acidic paper machines or open cooling water systems, preferably in amounts of 5 to 25 ppm.